import java.util.Scanner;

// 定义抽象类Shape  
abstract class Shape {
    abstract double area();
}

// 定义圆类Circle，继承自Shape  
class Circle extends Shape {
    private double radius;

    // 构造函数  
    public Circle(double radius) {
        this.radius = radius;
    }

    // 实现area方法  
    @Override
    double area() {
        return Math.PI * radius * radius;
    }
}

// 主程序  
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // 输入圆的半径  
        double radius = scanner.nextDouble();

        // 创建Circle实例  
        Circle circle = new Circle(radius);

        // 输出圆的面积  
        System.out.printf("area=%.1f%n", circle.area());
    }
}